1) Field do the Invention
The present invention relates to polymer nanocomposites and, more particularly to polymer nanocomposites having a synthesized dispersed phase. The present invention also relates to a method for producing the above polymer nanocomposites.
2) Description of the Prior Art
Modern applications of polymers are quite demanding and very often the properties of pure materials fail to satisfy their requirements. Polymer nanocomposites (PNCs) consist essentially of inorganic particles with nanometric dimensions dispersed in a single phase or multiphase polymer matrix. They combine the advantages of both classes of materials and widen their application range. Due to their high aspect ratio (typically larger than 50 to 100), volume fractions of inorganic nanoparticles as small as 2 to 7 wt % are enough to impact the PNCs with mechanical properties similar to those obtained upon 30 to 50 wt % addition of glass fiber, without greatly altering the density and the transparency of the matrix.
The most commonly used nanoparticles are made of clays and other lamellar materials with a close composition, for example double hydroxide lamellar compounds (hydrotalcites). For example, nanoparticles made of clay of sodium Montmorillonite class (Na-MMT) that are commercialized in the form of micronic agglomerates of lamellae structured in the form of sandwich-type structure with a thickness of 0.3-1 nm and a length of 50-100 nm for each layer have been used. A dispersion of nanometric layers in the host polymer matrix is obtained in two steps: 1) intercalation and 2) exfoliation. First, a swelling agent, usually a cationic or neutral surfactant, is introduced in intercalation position between the layers, increasing the interlamellar spacing. Shearing stresses are then applied on the intercalated clays which are incorporated into the polymer matrix causing clay exfoliation. Clay leaves with a nanometric thickness are thus well dispersed inside the polymer matrix.
PNCs have been made with a large variety of polymers such as polypropylene, polyethylene, polystyrene, polycarbonate, polyethylene oxide, polyacrylate, polyethylene terephthalate (PET), unsaturated polyester, polyurethane, phenolic and epoxy resins, ethylene vinyl acetate (EVA), styrene butadiene (SBR), acrylonitrile-butadiene-styrene (ABS), polybenzoxazole, polyetherimide, and nylon 6.
The performance of multiphase materials depends on the component properties, composition, structure, particle-particle, and particle-matrix interactions. High barrier, conductive and thermal resistance properties have been reported for PNCs without changing the classical machinery used for thermoplastics. However, the ultimate properties of such PNCs are restricted by the limited intrinsic properties of clays that are difficult to modify due to the high interaction energy between the individual layers.
Well-known in the catalyst field, synthetic nanoparticles are obtained by self-assembly of surfactant molecules that self-organize in supramolecular structures, i.e. liquid crystals assembly of cylindrical, spherical or lamellar micelles. These supramolecular structures may act as templates for mesostructured inorganic materials. Based on this concept, several ordered mesostructured and mesoporous inorganic materials with hexagonal, cubic, and lamellar symmetries were obtained. For the catalyst field, hexagonal and cubic structures are the most interesting since it is possible to extract the surfactant by calcination or ion exchange. The lamellar structure is the easiest to obtain. However, researchers working in the catalysis field tend to avoid this structure with low surface area which frequently collapses when extracting the surfactant. In the PNC field, this structure is suitable due to its high aspect ratio.